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<a href="#func-members">Functions</a> &#124;
<a href="#var-members">Variables</a>  </div>
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<div class="title">System and Clock Configuration</div>  </div>
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<p>Functions for system and clock setup available in system_<em>device</em>.c.  
<a href="#details">More...</a></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a>
Functions</h2></td></tr>
<tr class="memitem:ga93f514700ccf00d08dbdcff7f1224eb2"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2">SystemInit</a> (void)</td></tr>
<tr class="memdesc:ga93f514700ccf00d08dbdcff7f1224eb2"><td class="mdescLeft">&#160;</td><td class="mdescRight">Function to Initialize the system.  <a href="#ga93f514700ccf00d08dbdcff7f1224eb2">More...</a><br/></td></tr>
<tr class="separator:ga93f514700ccf00d08dbdcff7f1224eb2"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:gae0c36a9591fe6e9c45ecb21a794f0f0f"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f">SystemCoreClockUpdate</a> (void)</td></tr>
<tr class="memdesc:gae0c36a9591fe6e9c45ecb21a794f0f0f"><td class="mdescLeft">&#160;</td><td class="mdescRight">Function to update the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>.  <a href="#gae0c36a9591fe6e9c45ecb21a794f0f0f">More...</a><br/></td></tr>
<tr class="separator:gae0c36a9591fe6e9c45ecb21a794f0f0f"><td class="memSeparator" colspan="2">&#160;</td></tr>
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="var-members"></a>
Variables</h2></td></tr>
<tr class="memitem:gaa3cd3e43291e81e795d642b79b6088e6"><td class="memItemLeft" align="right" valign="top">uint32_t&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a></td></tr>
<tr class="memdesc:gaa3cd3e43291e81e795d642b79b6088e6"><td class="mdescLeft">&#160;</td><td class="mdescRight">Variable to hold the system core clock value.  <a href="#gaa3cd3e43291e81e795d642b79b6088e6">More...</a><br/></td></tr>
<tr class="separator:gaa3cd3e43291e81e795d642b79b6088e6"><td class="memSeparator" colspan="2">&#160;</td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Description</h2>
<p>Arm provides a template file <b>system_<em>device</em>.c</b> that must be adapted by the silicon vendor to match their actual device. As a <b>minimum requirement</b>, this file must provide:</p>
<ul>
<li>A device-specific system configuration function, <a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2">SystemInit()</a>.</li>
<li>A global variable that contains the system frequency, <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>.</li>
</ul>
<p>The file configures the device and, typically, initializes the oscillator (PLL) that is part of the microcontroller device. This file might export other functions or variables that provide a more flexible configuration of the microcontroller system.</p>
<dl class="section note"><dt>Note</dt><dd>Please pay special attention to the static variable <code>SystemCoreClock</code>. This variable might be used throughout the whole system initialization and runtime to calculate frequency/time related values. Thus one must assure that the variable always reflects the actual system clock speed. Be aware that a value stored to <code>SystemCoreClock</code> during low level initializaton (i.e. <code><a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2" title="Function to Initialize the system. ">SystemInit()</a></code>) might get overwritten by C libray startup code and/or .bss section initialization. Thus its highly recommended to call <a class="el" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f">SystemCoreClockUpdate</a> at the beginning of the user <code>main()</code> routine.</dd></dl>
<h1><a class="anchor" id="system_init_code_ex_sec"></a>
Code Example</h1>
<p>The code below shows the usage of the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a> and the functions <a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2" title="Function to Initialize the system. ">SystemInit()</a> and <a class="el" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f" title="Function to update the variable SystemCoreClock. ">SystemCoreClockUpdate()</a> with an LPC1700.</p>
<div class="fragment"><div class="line"><span class="preprocessor">#include &quot;LPC17xx.h&quot;</span></div>
<div class="line"></div>
<div class="line">uint32_t coreClock_1 = 0;                       <span class="comment">/* Variables to store core clock values */</span></div>
<div class="line">uint32_t coreClock_2 = 0;</div>
<div class="line"></div>
<div class="line"></div>
<div class="line"><span class="keywordtype">int</span> main (<span class="keywordtype">void</span>)  {</div>
<div class="line"></div>
<div class="line">  coreClock_1 = <a class="code" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>;                <span class="comment">/* Store value of predefined SystemCoreClock */</span></div>
<div class="line"></div>
<div class="line">  <a class="code" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f">SystemCoreClockUpdate</a>();                      <span class="comment">/* Update SystemCoreClock according to register settings */</span></div>
<div class="line"></div>
<div class="line">  coreClock_2 = <a class="code" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>;                <span class="comment">/* Store value of calculated SystemCoreClock */</span></div>
<div class="line"></div>
<div class="line">  <span class="keywordflow">if</span> (coreClock_2 != coreClock_1)  {            <span class="comment">/* Without changing the clock setting both core clock values should be the same */</span> </div>
<div class="line">    <span class="comment">// Error Handling</span></div>
<div class="line">  }</div>
<div class="line"></div>
<div class="line">  <span class="keywordflow">while</span>(1);</div>
<div class="line">}</div>
</div><!-- fragment --> <h2 class="groupheader">Function Documentation</h2>
<a class="anchor" id="gae0c36a9591fe6e9c45ecb21a794f0f0f"></a>
<div class="memitem">
<div class="memproto">
      <table class="memname">
        <tr>
          <td class="memname">void SystemCoreClockUpdate </td>
          <td>(</td>
          <td class="paramtype">void&#160;</td>
          <td class="paramname"></td><td>)</td>
          <td></td>
        </tr>
      </table>
</div><div class="memdoc">
<p>Updates the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a> and must be called whenever the core clock is changed during program execution. The function evaluates the clock register settings and calculates the current core clock. </p>

</div>
</div>
<a class="anchor" id="ga93f514700ccf00d08dbdcff7f1224eb2"></a>
<div class="memitem">
<div class="memproto">
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          <td class="memname">void SystemInit </td>
          <td>(</td>
          <td class="paramtype">void&#160;</td>
          <td class="paramname"></td><td>)</td>
          <td></td>
        </tr>
      </table>
</div><div class="memdoc">
<p>Initializes the microcontroller system. Typically, this function configures the oscillator (PLL) that is part of the microcontroller device. For systems with a variable clock speed, it updates the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>. SystemInit is called from the file <b>startup<em>_device</em></b>. </p>

</div>
</div>
<h2 class="groupheader">Variable Documentation</h2>
<a class="anchor" id="gaa3cd3e43291e81e795d642b79b6088e6"></a>
<div class="memitem">
<div class="memproto">
      <table class="memname">
        <tr>
          <td class="memname">uint32_t SystemCoreClock</td>
        </tr>
      </table>
</div><div class="memdoc">
<p>Holds the system core clock, which is the system clock frequency supplied to the SysTick timer and the processor core clock. This variable can be used by debuggers to query the frequency of the debug timer or to configure the trace clock speed.</p>
<dl class="section attention"><dt>Attention</dt><dd>Compilers must be configured to avoid removing this variable in case the application program is not using it. Debugging systems require the variable to be physically present in memory so that it can be examined to configure the debugger. </dd></dl>

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